Terminal construction

ABSTRACT

A terminal clamp for effecting an electrical connection with a conductor is disclosed. The terminal clamp includes first and second planar clamping surfaces for receiving a cylindrical wire conductor therebetween with the first clamping surface being defined by the head portion of a screw threaded into the second clamping surface. The second clamping surface is provided with a V-shaped slot which extends in the axial direction of the conductor clamped between these surfaces and which is dimensioned so that substantial portions of the conductor are coined into the slot when clamping pressure is applied to the conductor to more effectively retain the conductor at the terminal.

United States Patent [191 Snider Jan. 15, 1974 [73] Assignee: Therm-O-Disc Incorporated,

Mansfield, Ohio [22] Filed: May 5, 1972 [21] Appl. No.: 250,737

[56] References Cited UNITED STATES PATENTS ,l5l.674 3/1939 Adam et al. 339/269 .474,383 10/1969 Mahon et al 339/246 FOREIGN PATENTS OR APPLICATIONS 473,658 3/1929 Germany 339/269 366,079 l/l963 Switzerland 339/246 Primary ExaminerJoseph H. McGlynn Att0rney-I-Iarold F. McNenny et a].

[57] ABSTRACT A terminal clamp for effecting an electrical connection with a conductor is disclosed. The terminal clamp includes first and second planar clamping surfaces for receiving a cylindrical wire conductor therebetween with the first clamping surface being defined by the head portion of a screw threaded into the second clamping surface. The second clamping surface is provided with a V-shaped slot which extends in the axial direction of the conductor clamped between these surfaces and which is dimensioned so that substantial portions of the conductor are coined into the slot when clamping pressure is applied to the conductor to more effectively retain the conductor at the terminal.

8 Claims, 5 Drawing Figures TERMINAL CONSTRUCTION BACKGROUND OF THE INVENTION This invention relates to terminal clamps and, more particularly, to terminal clamps of the type which are provided on thermostats or terminal blocks. Conductors are often affixed to terminal posts by first crimping a connector onto the bared end of a conductor and then attaching the connector to the terminal post. Such connectors are usually flat ring tongue, flanged spade, or hook connectors which engage the terminal post screw and which are then clamped by the head of the screw. These connectors are flat and provide a relatively large clamping surface.

However, in many instances it is desirable and more efficient to merely insertthe bared end of the conductor between the clamping surfaces of the terminal clamp and then tighten the screw. If the conductor is a relatively heavy gauge, non-stranded cylindrical con ductor, the least assembly effort and cost are required when the wire end is merely inserted axially between the clamping surfaces without any wrapping about the terminal post, which would tend to retain the conductor at the terminal. Since there is very little frictional contact between a cylindrical conductor and planar clamping surfaces, such conductors tend to be easily separated from the terminal when the conductor is twisted or pulled axially. This problem is particularly acute where thermostats are wired with relatively heavy gauge wire. For example, many hot water heater thermostats require AWG wire which is connected at one end to the terminals of the thermostat and at the other end to another thermostat, a heater, or to the main power line. The installer frequently must twist or pull the heavy wire to effect the second connection, and such movements tend to loosen or separate the first connection.

To overcome these problems, it has been proposed that at least one of the clamping surfaces be provided with notches or serrations which are transverse to the axis of the conductor to bite into the conductor and, thereby, to more effectively retain the conductor at the terminal. Such an arrangement is shown, for example, in U. S. Pat. Nos. 3,191,140 and 2,304,711. While such constructions tend to provide a more positive grip on the conductor, they have not been entirely acceptable, since such transverse grooves do not substantially increase the area of frictional contact between the conductor and the clamping surfaces, and do not provide effective resistance to twisting forces.

Other prior art arrangements provide structures which do tend to increase the area of frictional contact, but which do not provide surface which will bite into the conductor to provide a positive lock. It is desirable to at least penetrate the oxidized surface of the conductor if the oxide surface of the conductor is not removed prior to installation to minimize areas of high resistance between the conductor and the terminal. An example of a terminal clamp which provides an increased area of contact between the conductor and a clamping surface may be found in US. Pat. No. 2,693,586, wherein the patentee provides a groove in a clamping surface which is adapted to receive a cylindrical portion of the bared end of the conductor. Another example of providing increased areas of surface contact between the conductor and the terminal may be found in U. S. Pat.

No. 3,248,684, wherein the patentee provides curved clamping surfaces which are adapted to embrace substantial portions of the cylindrical periphery of the conductor. It should be noted that in [1.5. Pat. No. 3,248,684, serrations are provided in the clamping surfaces which are intended to bite through the oxide layer of the conductor, but which are not intended to bite into the base metal of the conductor to provide a retaining function. Terminals having clamping surfaces which conform to the shape of the conductor are not only difficult to machine, but also are adapted to accommodate only conductors of a particular gauge.

SUMMARY OF THE INVENTION This invention overcomes the aforementioned prior art problems by providing an inexpensive terminal clamp which is adapted to accommodate a variety of conductor sizes and which is adapted to not only bite through the oxide coating on the conductor but to bite into the base metal of the conductor itself to provide a more positive gripping function and increased surface area contact between the clamping surfaces and the conductor. According to this invention, a planar clamping surface is provided with a groove or notch which has edges adapted to bite into the base metal of the conductor.

In the illustrated embodiment, the planar surface is provided with a longitudinal groove and laterally extending grooves. Each groove is proportioned to cut into the wire and is arranged so that the wire material is coined into the grooves to ensure a good electrical connection and to provide an interlocking joint which resists loosening when the wire is pulled or twisted.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a thermostat having terminals according to this invention, showing the bared end of a conductor assembled to one of the terminals, and with some terminal screws removed to show details of construction.

FIG. 2 is a cross sectional view, the plane of the section being indicated by the line 22 in FIG. ll.

FIG. 3 is a fragmentary, perspective view of a lower clamping member having a surface produced in accordance with the teachings of this invention.

FIG. 4 is an enlarged cross sectional view of a conductor and clamping surfaces showing the coaction between the conductor and surfaces when the conductor is clamped.

FIG. 5 is a fragmentary, perspective view of a conductor showing portions of the conductor deformed by a clamping surface groove according to this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, and particularly to FIGS. 1 and 2, there is illustrated a manual reset thermostat 10 which includes terminals produced in accordance with this invention. The thermostat 10 is described in greater detail in the copending application of Donald E. Place, Ser. No. 117,239, filed Feb. 22, 1971, now US. Pat. No. 3,675,178. Although this invention is illustrated in combination with a particular thermostat, it should be appreciated that the invention may be employed to effect electrical terminal connections on other devices and other thermostats. The thermostat 10 includes a plurality of terminal clamps 11, each of which is adapted to securely fasten a bared end portion 12 of a conductor 13 to the thermostat so that an electrical connection is effected.

The terminal clamp 11 includes first and second clamping surfaces 14 and 15, which respectively comprise the bottom surface of a headed screw 16 and a cooperating planar surface of a headed screw 16 and a cooperating planar surface of a terminal member 17. The headed screw 16 is threaded into an opening 18 in the surface so that clamping pressure may be applied to the bared end portion 12 of the conductor 13.

In order to more securely retain the portion 12 of the conductor 13 at the terminal 17, longitudinally extending notches or V-shaped grooves 19 are coined or stamped into the clamping surface 15. The grooves 19 are sized and shaped so that they provide spaced and parallel cutting or biting edges 21 where the diverging side walls 20 of the grooves 19 intersect the surface 15. A spacing of the edges is sufficiently small compared to the diameter of the wire to be connected so that they engage the wire adjacent to the bottom thereof and cut into the material of the wire as best illustrated in FIG. 4. Also the depth of the groove is proportioned so that wire material is coined into the groove as the edges cut When the screw 16 is tightened down against the wire, the edges 21 cut into the wire and a portion 22 of the wire material is coined into the groove. The opposed groove surfaces 20 converge in a direction away from the edges 21 and these surfaces cause the sides 23 of the coined portion 22 to be pressed inwardly with a wiping action that ensures a clean high pressure contact between the sides 23 and the groove surface 20. This ensures a good electrical connection.

In the preferred embodiment, a surface 15 is also provided with lateral grooves 26 which are spaced along the longitudinal grooves 19 and extend thereacross. These grooves also provide cutting edges 27 similar to the cutting edges 21 and converging side walls 28. The action of these cutting edges and side walls is similar to the action of the corresponding parts of the longitudinal groove 19 in that wire material is coined down into the grooves 26 to form lateral portions 29 intersecting the portion 22, as best illustrated in FIG. 5. The interfacial contact between the sides of the portions 22 and 29 and the associated grooves provides an interlocking mechanical joint between the wire and the terminal structure, which not only functions to increase the quality of the electrical connection but also functions to prevent the wire from twisting out or pulling out after the connection is made. The interfacial contact within the groove 19 resists twisting movement of the wire with respect to the terminal and the interfacial contact between the lateral portions 29 and the grooves 26 resist axial pull on the wire.

It is important to proportion the spacing between the edges 21 and the diameter of the wire such that when the wire is clamped, sufficient coining will occur to cause the portions 29 to extend into the lateral grooves. If the width of the grooves 19 is too great with respect to the wire diameter, the surfaces 20 tend to engage the wire tangentially and the desired cutting and coining action is not obtained. Similarly, the tendency of the wire to be coined into the lateral grooves 26 is minimized. On the other hand, if the lateral spacing between the edges 21 is too small, the coined portion 22 will not have sufficient width to provide the desired strength to resist the twisting forces that may be applied to the wire.

Preferably, the width of the grooves is between about 30 percent to 50 percent of the diameter of the wire to be connected when the included angle is about For example, a groove 0.030 inches in width having a 90 included angle has been successfully used with solid wire sizes from No. 10 to 14. The underside of the head of the screw is relieved inwardly of a skirt portion 31, as illustrated at 32, to produce a concentration of the clamping force over a relatively small area, which causes the skirt to deform the adjacent surfaces of the wire and also to form an interlocking joint which cooperates with the grooves 19 and 26 to resist loosening caused by either twisting or pulling of the wire.

In order to ensure that the conductor 13 will be axially aligned and in contact with the slot 19, the terminal clamp is provided with fencing means which comprises upstanding projections 25 located on opposite sides of each terminal member 17. The fencing means also includes the shank of each headed screw 16. The fencing means does not have to positively position the wire in exact alignment with the groove so long as it positions the wire so that it will move into the groove as the screw is tightened.

Although a preferred embodiment of this invention is illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention claimed herein.

1 claim:

1. A terminal clamp for a conductor comprising first and second substantially planar clamping surfaces, said surfaces being movable toward each other to clamp a conductor therebetween, fencing means for axially guiding said conductor to a position between said surfaces wherein the axis of the conductor is substantially parallel to said fencing means, first groove means in one of said planar members substantially parallel with said fencing means, and therefore with the axis of the conductor to be clamped, said first groove means and said one of said planar surfaces defining edges which are adapted to bite into said conductor so that substantial portions of said conductor will be coined into said first groove means when said surfaces are moved toward each other to clamp the conductor, and second groove means in said one of said planar members normal to said first groove means.

2. A terminal clamp according to claim 1, wherein said first and second groove means are in said second surface, wherein said clamp includes a headed screw threaded into said second surface, and wherein said first surface comprises the bottom surface of the screw head.

3. A terminal clamp according to claim 2, wherein said first groove means is a V-shaped notch.

4. A terminal clamp according to claim 3, wherein said edges are spaced apart a distance which is about 30 percent to 50 percent of the diameter of a conductor to be connected and the notch has about a 90 included angle.

5. A terminal assembly comprising first and second substantially planar clamping surfaces, said surfaces being movable toward each other to clamp a conductor therebetween, first groove means in one of said surfaces, a cylindrical wire clamped between said clamping portions, said cylindrical wire having its longitudi- 7. A terminal assembly according to claim 6, wherein said first groove means is a V-shaped slot and wherein the side walls of said slot are non-tangential to said cylindrical wire.

8. A terminal clamp according to claim 7, wherein said edges are spaced apart a distance which is about 30 percent to 50 percent of the diameter of a conductor to be connected and said slot has about a included angle. 

1. A terminal clamp for a conductor comprising first and second substantially planar clamping surfaces, said surfaces being movable toward each other to clamp a conductor therebetween, fencing means for axially guiding said conductor to a position between said surfaces wherein the axis of the conductor is substantially parallel to said fencing means, first groove means in one of said planar members substantially parallel with said fencing means, and therefore with the axis of the conductor to be clamped, said first groove means and said one of said planar surfaces defining edges which are adapted to bite into said conductor so that substantial portions of said conductor will be coined into said first groove means when said surfaces are moved toward each other to clamp the conductor, and second groove means in said one of said planar members normal to said first groove means.
 2. A terminal clamp according to claim 1, wherein said first and second groove means are in said second surface, wherein said clamp includes a headed screw threaded into said second surface, and wherein said first surface comprises the bottom surface of the screw head.
 3. A terminal clamp according to claim 2, wherein said first groove means is a V-shaped notch.
 4. A terminal clamp according to claim 3, wherein said edges are spaced apart a distance which is about 30 percent to 50 percent of the diameter of a conductor to be connected and the notch has about a 90* included angle.
 5. A terminal assembly comprising first and second substantially planar clamping surfaces, said surfaces being movable toward each other to clamp a conductor therebetween, first groove means in one of said surfaces, a cylindrical wire clamped between said clamping portions, said cylindrical wire having its longitudinal cylindrical axis parallel to the longitudinal axis of said first groove means and having substantial portions thereof coined into said first groove means, and second groove means in said one of said surfaces normal to said first groove means.
 6. A terminal assembly according to claim 5, wherein said first and second groove means are in said second surface, wherein said clamp includes a headed screw threaded into said second surface, and wherein said first surface comprises the bottom surface of the screw head.
 7. A terminal assembly according to claim 6, wherein said first groove means is a V-shaped slot and wherein the side walls of said slot are non-tangential to said cylindrical wire.
 8. A terminal clamp according to claim 7, wherein said edges are spaced apart a distance which is about 30 percent to 50 percent of the diameter of a conductor to be connected and said slot has about a 90* included angle. 